April in the hills with Barbara Mitcalfe and Chris Horne

Dacrydium cupressinum, rimu

Rimu’s long, pendulous branchlets Photo: JEREMY ROLFE

Rimu's ancestry dates from c. 37 million years ago. It is an endemic NZ conifer member of the podocarp family, found in the North, South and Stewart islands, from sea level up to c. 700 m, with a lifespan of c. 700 to c. 1000 years. It has a conical form as a young adult and can grow to more than 60 m high, with a trunk of up to c. 2 m diameter. Its brown bark falls off in slabs, often c. 30 x 50 cm, revealing an attractive pattern underneath, like ripple marks on sand.

Juvenile rimu leaves are scale-like, 4-7 x 0.5–1 mm, strongly keeled on the underside and angled away from the stem. Adult leaves are similar, but only 2–3 mm. long. Note that unlike kahikatea leaves, they are prickly, and pendulous on long, flexible branchlets. This is a key difference between rimu and kahikatea. (See image). Pollination and fertilisation in rimu are similar to kahikatea in all respects, including time taken to mature. (Please refer to the March Tramper article).

Use

Māori found a multitude of uses for rimu. The heartwood was used for making spears up to 6 m long, and bundles of the highly resinous scraps were bound together and lit for torches. They used the timber for making handles for a range of tools such as toki / adzes. They even used the soot from the burnt heartwood, as pigment for moko / tattoo. Medicinal uses / rongoā, included drinking the liquid in which pieces of rimu bark had been boiled, a proven cure for dysentery. The gum was used to staunch bleeding.

In 1777 Captain Cook recorded boiling up a brew of rimu and mānuka foliage with molasses, and fermenting it with yeast, as an experimental remedy for scurvy. Not surprisingly this 'medicine' proved very popular with his crew.

In the March article, you will have read about the tiny, juicy kahikatea female cones collected en masse in season by Māori, for sweet food. Female rimu cones were similarly enjoyed in season. They are also an essential food for the endangered kākāpō, to the extent that rimu and kākāpō appear to be interdependent. Rimu cones, abundant in a mast year, are rich in protein, essential fatty acids, carbohydrates, sugar, and particularly calcium, essential for strong egg shells, and for developing strong bones in the chicks. Kākāpō, being vegetarian, have no other source of calcium. When there is a poor crop of rimu cones, DOC supplies special supplementary food, replicating the nutritional values of the cones.

Continuing the theme of rimu usage, hundreds of thousands of NZ homes were built with rimu's superior quality timber - hard, strong and durable. For many decades it has been the main timber for house frames, weatherboards, doors, door frames, panelling, flooring, furniture, and plywood veneers. The beautifully figured heartwood is sought after for decorative uses, as in Wellington's Beehive. Now in short supply, rimu timber is often rescued from former usage and recycled